Without limiting the scope of the invention, its background is described in connection with aircraft dampers.
One such patent is U.S. Pat. No. 8,622,375, issued to Bosworth, et al. and entitled, “Dual frequency damper for an aircraft”. Briefly, these inventors teach a dual frequency damper includes a liquid inertia vibration eliminator (LIVE) portion and a fluid damper portion. The LIVE portion and fluid damper portion are said to operate in series and function so that dual frequency damper is optimized in both stiffness and damping at multiple frequencies. LIVE portion acts as a frequency dependent switch to selectively cause low frequency oscillatory forces to be treated primarily by the high spring rate and high damping rate characteristics of the fluid damper portion, and also to select high frequency oscillatory forces to be primarily treated by the low spring rate and low damping rate characteristics of the LIVE unit portion.
One such patent application is U.S. Patent Publication No. 2015/0369326, filed by Modrezejewski, et al., and entitled “Rotating Shaft Damping With Electro-Rheological Fluid”. Briefly, these applicants teach rotating shaft damping using an electro-rheological fluid. At least a portion of a circumferential surface area of a portion of a rotorcraft rotating shaft is surrounded with multiple hollow members, and each hollow member includes an electro-rheological fluid having a viscosity that changes based on an electric field applied to the electro-rheological fluid. The vibration of the rotorcraft rotating shaft is controlled by changing the viscosity of the electro-rheological fluid in response to the electric field applied to the electro-rheological fluid.
Yet another application is U.S. Patent Publication No. 2008/0173754, filed by Strehlow, et al., and is entitled “Method For Damping Rear Extension Arm Vibrations Of Rotorcraft And Rotorcraft With A Rear Extension Arm Vibration Damping Device”. Briefly, these applicants are said to teach a method for damping vibrations in a tail boom of a rotary-wing aircraft includes the steps of detecting tail boom vibrations induced by external vibration excitation, and generating and introducing strains into the tail boom based on the detected tail boom vibrations. Next, strains are applied over a surface area and are out-of-phase with respect to the detected tail boom vibrations so as to damp the externally excited induced tail boom vibrations. In addition, a rotary-wing aircraft, includes a fuselage, a cockpit area integrated into the fuselage, a tail boom arranged on the fuselage and a tail boom vibration-damping device. The vibration-damping device includes at least one sensor element configured to detect tail boom vibrations induced by external vibration excitation and at least one actuator configured to generate and introduce strains into the tail boom that are out-of-phase with respect to the induced tail boom vibrations, the actuator being functionally coupled to the sensor element, engaging with a tail boom structure at one side of the tail boom, and forming a flat-surfaced bond with the tail boom.